1. Field of the Invention
This invention relates to a circuit for controlling the operation of a device based at least partly on sensing a fluid level; and more particularly, relates to a circuit board for controlling a pump based at least partly on sensing a fluid level.
2. Description of Related Art
Touch sensitive technology is known in the art and available in the marketplace. For example, one company, known as Touch Sensor, provides touch sensitive technology that is based at least partly on using an application specific integrated circuit (ASIC) device. For a particular application, the ASIC device and related components are required for each TouchCell™, which is basically a sensing pad that detects if a person's finger, or an aqueous solution, or a conductive mass is touching the dielectric substrate to which the TouchCell™ is attached behind. Each TouchCell™ has only two possible output states—“activated” and “not activated.” Based on a present understanding, it seems that the output state depends on a threshold at the input, once the input is over or under that threshold the output state will reflect it. Moreover, Touch Sensor's product is focused on the ASIC and related hardware; they describe their product as “a software free, solid-state switch.” The design and manufacturing are done by Touch Sensor based on costumer specifications.
In comparison, another company, know as Atmel, provides touch sensitive technology that is based on using a software library that can be downloaded into their microcontrollers and performs the tasks related to the processing of the signals from the sensing pads, so there is proprietary hardware involved. However, Atmel's product seems to be more flexible, from the user's point of view, because the user can buy Atmel's microcontrollers, download the software library and proceed to design and manufacture the hardware. Each sensing pad has only two states associated to it, “activated” and “not activated”, just like the Touch sensor's product.
Some disadvantages of the known prior art products include the following:
1) Any developed application is tied to proprietary hardware/software.
2) There is not intermediate or proportional responses from the sensing pads. Because of the second disadvantage, multiple sensing pads and microcontroller inputs are required to perform level detection; so the cost increases with the number of sensing pads; no distinction can be made between different types of materials; and only electrically conductive materials can be detected.
3) At least one microcontroller input is required for each sensing pad.
4) There are some location restrictions regarding the separation between the supporting hardware and the sensing pads.
Moreover, U.S. Pat. No. 5,153,572 discloses touch sensitive technology that includes a touch control circuit having an oscillator with a positive plate of a capacitor connected to an inverting input of a comparator, and includes resistors configured in relation to the inverting input, the non-inverting input and the output of the comparator, for providing a square wave output. A touch panel has on/off touch pads arranged in relation to pads and coupled to a connector. The square wave output is provided from the connector to the pads. In operation, the on/off touch pads are contacted in order to make a selection. The on/off touch pads are not directly connected to the positive plate of the capacitor which is directly connected to the inverting input of the comparator of the oscillator; instead, the square wave signal is coupled to the on/off touch pads via the connector, the pads, an adhesive and a glass element. Further, the touch-sensitive control circuit for touch pads also has a coincidence detector responding to simultaneous change of impedance of two or more different touch pads using logic circuits.